Actuator, optical scanner and image forming apparatus

ABSTRACT

An actuator includes a mass section; a support section; a coupling section for coupling the mass section rotatably to the support section so as to support the mass section with cantilever structure; and a pair of driving sources including a piezoelectric element for rotating the mass section, wherein the pair of driving sources are provided separately from each other with respect to a central axis of rotation of the mass section, each of the driving sources is provided slidably with respect to the coupling section or the support section, and the actuator is structured such that it causes the pair of piezoelectric elements to expand and contract in phases opposite to each other, so as to rotate at least a part of the coupling section while torsionally deforming the mass section.

BACKGROUND

1. Technical Field

The present invention relates to an actuator, an optical scanner and animage forming apparatus.

2. Related Art

As an optical device for drawing by optical scanning using a laserprinter or the like, various devices have been known in the related art.These devices include an optical device which uses an actuator includinga torsional vibrator. (JP-A 2004-191953 is an example of related art.)

JP-A-2004-191953 discloses an actuator including a torsional vibrator ofone-degree-of-freedom vibration system. The actuator includes areflective mirror, a fixed frame section for supporting the reflectivemirror, and a pair of spring sections for coupling the reflective mirrorto the fixed frame section. The pair of spring sections are provided soas to support the reflective mirror from the both sides of thereflective mirror.

Each of the spring sections has a first spring section for coupling thereflective mirror to the coupled body and a second spring section forcoupling the fixed frame section to the coupled body. In addition, thesecond spring section includes a pair of elastic bodies which areprovided so as to be opposed to each other with respect to a centralaxis of rotation. That is, the spring section is structured such thatthe spring is branched into two at a middle point thereof.

To each of the second spring sections, there is joined a piezoelectricelement (driving source) such that it expands and contracts in thelongitudinal direction thereof. The actuator applies voltage to thepiezoelectric element and causes the piezoelectric element to expand andcontract, causing bending deformation of the second spring section.Along with the deformation, the actuator torsionally deforms the firstspring section so as to rotate the reflective mirror, and reflects andscans a light beam. This enables drawing by optical scanning.

In this case, since the piezoelectric element joined to each of thespring sections generates heat caused by driving (voltage application)thereof, the temperature at the spring section is forced to increase.The increase in temperature causes the spring section to expand.However, since the actuator according to JP-A-2004-191953 has adual-support beam (dual support) structure, it does not enablepermitting change in shape of the spring section caused by expansion.This results in a rapid change in a spring constant of the pair ofspring sections and distortion of the entire actuator, which disablesmaintaining stable driving of the actuator.

Particularly in the case where the actuator is used as an opticalscanner like the actuator in JP-A-2004-191953, the drawback as describedabove becomes notable. Specifically when the actuator scans a lightbeam, the reflective mirror reflects most of the irradiated light beam.However, it is impossible to make optical reflectivity by the reflectivemirror 100%. In such an actuator, a part of the light beam which hasbeen irradiated to the reflective mirror turns to heat, increasing thetemperature of the actuator. The increased temperature of the actuatorcauses the drawback as described above.

In addition, thermal expansion of the spring section caused by theincreased temperature displaces the central axis of rotation of thereflective mirror. This displacement results in a drawback that theactuator cannot have desired scan characteristics.

Based on what has been described above, the actuator according toJP-A-2004-191953 has a drawback that it cannot maintain desired scancharacteristics in the case where it is used for a long period of time.

SUMMARY

An advantage of the invention is to provide an actuator, an opticalscanner and an image forming apparatus which enables maintaining stabledriving thereof even in the case where it is used continuously for along period of time.

Such advantage is achieved by the inventions as described above.

According to an aspect of the invention, an actuator includes a masssection; a support section; a coupling section for coupling the masssection rotatably to the support section so as to support the masssection with cantilever structure; and a pair of driving sourcesincluding a piezoelectric element for rotating the mass section. In theactuator, the pair of driving sources are provided separately from eachother with respect to a central axis of rotation of the mass section,each of the driving sources is provided slidably with respect to thecoupling section or the support section, and the actuator is structuredsuch that it causes the pair of piezoelectric elements to expand andcontract in phases opposite to each other, so as to rotate at least apart of the coupling section while torsionally deforming the masssection.

This enables permitting displacement of the coupling section caused bythermal expansion in the direction parallel to the central axis ofrotation of the mass section. This results in preventing a rapid changein a spring constant of the coupling section, and further enableskeeping the central axis of rotation of the mass section fixed.Accordingly the actuator is capable of having desired vibrationcharacteristics, even in the case where heat generated by thepiezoelectric element has increased the temperature of the actuator.That is, the actuator is capable of maintaining desired vibrationcharacteristics even in the case where it is used continuously for along period of time.

It is preferable that, each of the driving sources be secured to thesupport section and further include a sliding member between thepiezoelectric element and the coupling section, and the sliding memberbe joined to the piezoelectric element on which it is provided and beslidable with respect to the coupling section.

Provision of such sliding members enables increasing the degree offreedom in design, such as a contact position between each of thedriving sources and the coupling section and a shape of the contactportion or the like, and enables achieving desired sliding performancebetween the coupling section and the each of the driving sources.

It is preferable that the sliding member has a lower heat conductivitythan a primary component of the piezoelectric element.

This enables suppressing transmission to the piezoelectric element ofheat generated from the piezoelectric element caused by applying voltage(i.e., causing the piezoelectric element to expand and contract). Thisresults in enabling suppressing the coupling section from beingdeformed.

It is preferable that surface treatment be provided on a surface of anabutting section of each of the driving sources with the couplingsection and/or a surface of the abutting section of the coupling sectionwith each of the driving sources to enhance sliding performance.

This enables enhancing sliding performance between the coupling sectionand the driving source.

It is preferable that the coupling section have a plate-shaped drivesection, a first elastic section for coupling the drive sectionrotatably to the first support section, and a second elastic section forcoupling the mass section rotatably to the drive section, and each ofthe driving sources be provided slidably with respect to the drivesection.

Such a structure enables causing the pair of driving sources to expandand contract in phases opposite to each other, rotating the drivesection while torsionally deforming the first elastic section, and,along with the rotation, rotating the mass section while torsionallydeforming the second elastic section. This results in making therotation angle of the mass section larger even in the case where therotation angle of the drive section is small.

It is preferable that each of the driving sources make a point contactwith the drive section, or make a line contact therewith so that itextends in a direction parallel to the central axis of rotation of themass section.

This enables, during rotation of the drive section, maintaining thecontact area between the drive section and the driving sourcesubstantially constant and smoothly rotating the drive section.

It is preferable that each of the driving sources makes a line contactwith the entire area of the central axis of rotation of the mass sectionin the direction parallel to the drive section.

This enables uniformly applying driving force of each driving sourcecaused by expansion and contraction each piezoelectric element on theentire area of the drive section in the direction parallel to thecentral axis of rotation of the mass section.

It is preferable that the pair of driving sources be providedsubstantially symmetrically with each other with respect to the centralaxis of rotation of the mass section in plan view of the drive section.

This enables rotating the drive sections symmetrically with each otherwith respect to the central axis of rotation of the mass section.

It is preferable that the elastic section have a pair of elasticallydeformable elastic members that are opposed to each other with respectto the central axis of rotation of the mass section, the pair of drivingsources be provided corresponding to the pair of elastic members, andthe driving source and the elastic member that correspond to each otherbe slidably provided.

Such a structure enables rotating the mass section while keeping thecentral axis of rotation fixed.

It is preferable that each of the driving sources make a point contactwith the elastic member.

This enables, during rotation of the drive section, maintaining thecontact area between the drive section and the driving sourcesubstantially constant and smoothly rotating the drive section.

The actuator according to any one of claims 1 to 10, wherein the masssection includes a light reflective section having light reflectivity

It is preferable that the mass section include a light reflectivesection having light reflectivity

This enables using the actuator as an optical device.

According to another aspect of the invention, an optical scannerincludes: a mass section; a support section; a coupling section forcoupling the mass section rotatably to the support section so as tosupport the mass section with cantilever structure; and a pair ofdriving sources including a piezoelectric element for rotating the masssection. In the optical scanner, the pair of driving sources areprovided separately from each other with respect to a central axis ofrotation of the mass section, each of the driving sources is providedslidably with respect to the coupling section or the support section,and the optical scanner is structured such that it causes the pair ofpiezoelectric elements to expand and contract in phases opposite to eachother, so as to rotate at least a part of the coupling section whiletorsionally deforming the mass section, and scans a light beam reflectedby the light reflective section.

This enables permitting displacement of the coupling section caused bythermal expansion in the direction parallel to the central axis ofrotation of the mass section. This results in preventing a rapid changein a spring constant of the coupling section, and further enableskeeping the central axis of rotation of the mass section fixed.Accordingly the optical scanner is capable of having desired vibrationcharacteristics, even in the case where heat generated by thepiezoelectric element has increased the temperature of the opticalscanner. That is, the optical scanner is capable of maintaining desiredvibration characteristics even in the case where it is used continuouslyfor a long period of time.

According to a further aspect of the invention, an image formingapparatus includes an optical scanner including: a mass section; asupport section; a coupling section for coupling the mass sectionrotatably to the support section so as to support the mass section withcantilever structure; and a pair of driving sources including apiezoelectric element for rotating the mass section. In the opticalscanner, the pair of driving sources are provided separately from eachother with respect to a central axis of rotation of the mass section,each of the driving sources is provided slidably with respect to thecoupling section or the support section, the scanner is structured suchthat it causes the pair of piezoelectric elements to expand and contractin phases opposite to each other, so as to rotate at least a part of thecoupling section while torsionally deforming the mass section, and scansa light beam by the light reflective section.

This enables providing an image forming apparatus having superiordrawing characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a perspective view showing Embodiment 1 of the actuatoraccording to the invention.

FIG. 2 is a sectional view cut along Line A-A in FIG. 1.

FIG. 3 is a sectional view cut along Line B-B in FIG. 1.

FIG. 4 is an expanded view of a driving source.

FIG. 5 is a drawing showing one example of a waveform of voltage fordriving the actuator shown in FIG. 1.

FIG. 6 is a diagram explaining a manufacturing method of the actuator.

FIG. 7 is a diagram explaining a manufacturing method of the actuator.

FIG. 8 shows Embodiment 2 of the actuator according to the invention.

FIG. 9 is a sectional view cut along Line A-A in FIG. 8.

FIG. 10 is an expanded view of a driving source.

FIG. 11 is a schematic view of a laser printer.

FIG. 12 is a schematic view of an exposure unit.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferable embodiments of an actuator according to the invention willnow be described with reference to the attached drawings.

Embodiment 1

First, Embodiment 1 of the actuator according to the invention will bedescribed.

FIG. 1 is a perspective view showing Embodiment 1 of the actuatoraccording to the invention, FIG. 2 is a sectional view cut along LineA-A in FIG. 1, FIG. 3 is a sectional view cut along Line B-B in FIG. 1,FIG. 4 is an expanded view of a driving source, and FIG. 5 is drawingshowing one example of a waveform of voltage for driving the actuatorshown in FIG. 1.

Hereinafter, for convenience of description, in FIG. 1, the front sideof a plane of the drawing will be referred to as “top,” the back sidethereof as “bottom,” the right side thereof as “right,” and the leftside thereof as “left.” In FIGS. 2 and 3, the top side of a plane of thedrawing will be referred to as “top,” the bottom side thereof as“bottom”, the right side thereof as “right,” and the left side thereofas “left.”

An actuator 1 has a base body 2 having a two-degree-of-freedom vibrationsystem as shown in FIG. 1, a pair of driving sources 4, 5 for drivingthe two-degree-of-freedom vibration system of the base body 2, and asupport substrate for supporting the driving sources 4, 5.

The base body 2 includes a plate-shaped mass section 21, a supportsection 22 for supporting the mass section 21, and a coupling section 24for supporting the mass section 21 with cantilever structure. Inaddition, the coupling section 24 includes a plate-shaped drive section241, a first elastic section 242, and a second elastic section 243. Thatis, the base body 2 includes the mass section 21, the support section22, the drive section 241, the first elastic section 242 and the secondelastic section 243.

In such an actuator 1, application of voltage to piezoelectric elements41, 51 which will be described later causes the piezoelectric elements41, 51 to expand and contract in phases opposite to each other (i.e., inthe opposite directions), and rotates the drive section 241 whiletorsionally deforming the first elastic section 242. Along with therotation, the actuator 1 rotates the mass section 21 while torsionallydeforming the second elastic section 243. At this time, the drivesection 241 and the mass section 21 are rotated centering around acentral axis X of rotation shown in FIG. 1, respectively.

On a top surface (that is, a surface opposite to the support substrate3) of the mass section 21, there is provided a light reflective section211 having light reflectivity.

The mass section 21 and the drive section 241 are provided such that thedrive section 241 is connected to the support section 22 via the firstelastic section 242, and the mass section 21 is connected to the drivesection 241 via the second elastic section 243.

The first elastic section 242 couples the drive section 241 to thesupport section 22 so as to make the drive section 241 rotatable withrespect to the support section 22.

The second elastic section 243 couples the mass section 21 to the drivesection 241 so as to make the mass section 21 rotatable with respect tothe drive section 241.

Such first elastic section 242 and second elastic section 243 arecoaxially provided, and they serve as the central axis of rotation X(axis of rotation), around which the drive section 241 is rotatable withrespect to the support section 22, and the mass section 21 is rotatablewith respect to the drive section 241.

In addition, the base body 2 has a first vibration system including thedrive section 241 and the first elastic section 242, and a secondvibration system including the mass section 21 and the second elasticsection 243. Specifically the base body 2 has a two-degree-of-freedomvibration system which includes the first vibration system and thesecond vibration system.

Such a two-degree-of-freedom vibration system is formed thinner than atotal thickness of the base body 2, and is located above the base body 2in the vertical direction in FIG. 2. In other words, on the base body 2,there is formed a portion which is thinner than the total thickness ofthe base body 2. The mass section 21, the drive section 241, the firstelastic section 242 and the second elastic section 243 are formed byformation of holes with different shapes in the thinner portion.

According to the Embodiment 1, since the top surface of the thinnerportion is located in the same plane as the top surface of the supportsection 22, a space (concave section) 28 for rotating the mass section21 and the drive section 241 is formed below the thinner portion.

Such base body 2 is primarily made of, for example, silicon, and isintegrally formed by the mass section 21, the drive section 241, thesupport section 22, the first elastic section 242 and the second elasticsection 243. As described above, use of silicon as the main materialenables achieving superior rotational characteristics and havingsuperior durability. In addition, this enables micro processing (ormicro fabrication) and reducing the size of the actuator 1.

Note that the base body 2 may have a structure such that the masssection 21, the drive section 241, the support section 22, the firstelastic section 242 and the second elastic section 243 are formed from asubstrate having a laminated structure such as a silicon-on-insulator(SOI) substrate. For doing this, it is preferable that the mass section21, a part of the support section 22, the drive section 241, the firstelastic section 242 and the second elastic section 243 are formed into asingle layer of a substrate with a laminated structure so that they areintegrated.

Such base body 2 is supported by the support substrate 3 primarily madeof, for example, glass or silicon.

In the support substrate 3, as shown in FIG. 3, there is formed anopening section 31 at a portion corresponding to the mass section 21.The opening section 31 serves as a relief section for preventing themass section 21 from being contacted with the support substrate 3 whilethe mass section 21 is being rotated (vibrated). Provision of theopening section (relief section) 31 enables preventing the size of theentire actuator 1 from being increased and enables an oscillating angle(amplitude) of the mass section 21 to be made larger.

Note that the relief section as described above need not be necessarilyreleased (opened) at the bottom surface (i.e., the surface opposite tothe mass section 21) of the support substrate 3 as long as the reliefsection has a structure having the advantageous effects as describedabove. Specifically the relief section may be formed by a concavesection formed on the top surface of the support substrate 3. Inaddition, the relief section need not be provided such as in the casewhere the depth of the space 28 of the mass section 21 is largercompared to the oscillating angle (amplitude) of the mass section 21.

In addition, on the support substrate 3, there are provided the pair ofdriving sources 4, 5 for rotating the mass section 21 at positions whichcorrespond to the drive section 241. Specifically the pair of drivingsources 4, 5 are provided between the drive section 241 and the supportsubstrate 3.

The driving source 4 and the driving source 5 are provided separatelyfrom each other with respect to the central axis X of rotation.Specifically in FIG. 2, the driving source 4 is provided to the left ofthe central axis X of rotation, and the driving source 5 is provided tothe right thereof.

The driving source 4 and the driving source 5 are respectively joined tothe support substrate 3, and are provided slidably with respect to thedrive section 241. As described above, the mass section 21 is supportedwith cantilever structure by the coupling section 24. Therefore, makingthe respective driving sources 4, 5 slidable with respect to the drivesection 241 (i.e., coupling section 24) permits displacement of thecoupling section 24 in a direction parallel to the central axis X ofrotation caused by thermal expansion. This enables preventing a rapidchange in a spring constant of the coupling section 24, and furtherkeeping the central axis X of rotation of the mass section 21 fixed.Accordingly the actuator 1 is capable of having desired vibrationcharacteristics even in the cases such as where a light beam exceedingthe light beam which was able to be reflected by the light reflectivesection 211 has increased the temperature of the actuator 1 or whereheat emitted by the piezoelectric elements 41, 42 has increased thetemperature of the actuator 1. That is, the actuator 1 is capable ofmaintaining desired vibration characteristics even in the case where itis used continuously for a long period of time.

The driving sources 4, 5 will now be described in details. Since thedriving source 4 and the driving source 5 have similar structures(including shapes and dimensions), explanation will be given on thedriving source 4 as a representative, and explanation on the drivingsource 5 will be omitted.

The driving source 4, as shown in FIG. 4, includes the piezoelectricelement 41 and the sliding member 42.

The piezoelectric element 41 has a columnar structure which expands andcontracts in the longitudinal direction thereof, and it is provided suchthat it expands and contracts in a direction perpendicular to a plane ofthe drive section 241 when the actuator 1 is not driven (i.e., in thevertical direction in FIG. 2). Furthermore, the bottom surface of thepiezoelectric element 41 is joined to the support substrate 3.

Such piezoelectric element 41, as shown in FIG. 4, has a piezoelectriclayer 411 mainly made of piezoelectric materials, and a pair ofelectrodes 412, 413 that sandwich the piezoelectric layer 411.

Examples of the piezoelectric materials which constitute thepiezoelectric layer 411 include zinc oxide, aluminum nitride, lithiumtantalate, lithium niobate, potassium niobate, lead zirconate titanate(PZT), barium titanate, and other various materials. One type may beused or more than one type may be combined for use for the piezoelectricmaterials. Particularly it is preferable that at least one of zincoxide, aluminum nitride, lithium tantalate, lithium niobate, potassiumniobate and lead zirconate titanate be mainly used. Forming thepiezoelectric layer 411 of such materials enables driving the actuator 1at a higher frequency

The electrode 412 is provided such that a part thereof is exposed fromthe bottom surface of the piezoelectric layer 411 (i.e., the lower endsurface in FIG. 4). The electrode 413 has the same shape as the topsurface of the piezoelectric layer 411 (i.e., the upper end surface inFIG. 3), and is provided on the top surface of the piezoelectric layer411. In addition, the electrode 413 is connected to a terminal 414provided on the support member 3 via a wiring formed by for example,wire bonding. In addition, the electrode 412 and the electrode 413(i.e., terminal 414) are respectively connected to a power source(voltage application means), not shown.

When voltage is applied to between the electrode 412 and the electrode413 (i.e., terminal 414), the piezoelectric layer 411 expands andcontracts in the longitudinal direction due to the piezoelectric effectthereof.

On the top surface of such piezoelectric element 41 (i.e., the surfaceopposite to the piezoelectric layer 411 of the electrode 413), there isprovided the sliding member 42. Specifically the sliding member 42 isprovided between the piezoelectric element 41 and the drive section 241.In addition, the sliding member 42 is joined to the piezoelectricelement 41, and is slidable with respect to the drive section 241.Provision of such sliding member 42 enables increasing the degree offreedom in design such as the contact position between the drivingsource 4 and the drive section 241, the shape of a contact portion orthe like, and enabling achieving desired sliding performance between thedrive section 241 and the driving source 4.

Although the sliding member 42 is joined to the piezoelectric element41, the sliding member 42 is not limited to this structure and mayinstead be joined to the drive section 241. However, joining the slidingmember 42 to the piezoelectric element 41 enables reducing the mass ofthe drive section 241 and rotating the drive section 241 at a higherspeed, compared to a case where the sliding member 42 is joined to thedrive section 241.

A distal end portion of the sliding member 42 (i.e, the end portion onthe drive section 241 side) serves as a contact portion with the drivesection 241, as shown in FIG. 1 or 3. The contact portion (i.e., distalend portion) is rounded in the direction perpendicular to the centralaxis X of rotation, as shown in FIG. 4. In this case, while the drivesection 241 is rotated around the central axis X of rotation, thedriving source 4 expands and contracts in the direction perpendicular tothe plane of the drive section 241 when the driving source 4 is notdriven. In other words, an angle created between the plane of the drivesection 241 and the direction in which driving source 4 expands andcontracts when the drive section 241 is rotated changes. That is, thecontact position of the drive section 241 with the sliding member 42slightly changes on the plane of the drive section 241 in the directionperpendicular to the central axis X of rotation. Therefore, rounding ofthe distal end portion enables enhancing following capability of thesliding member 42 with respect to rotation of the drive section 241.

The sliding member 42 makes a line contact with the drive section 241such that the sliding member 42 extends in a direction parallel to thecentral axis X of rotation. This enables maintaining a contact areabetween the drive section 241 and the sliding member 42 (driving source4) substantially constant during the rotation of the drive section 241.In addition, this enables preventing the position of the contact portionof the drive section 241 with the sliding member 42 from rapidlychanging during the rotation of the drive section 241. This results inenabling smoothly rotating the drive section 241 while keeping thecentral axis X of rotation fixed.

On the other hand, there are some cases where, for example, the distalend of the sliding member 42 is formed of a flat plane, and the flatplane of the sliding member 42 makes a plane contact with the drivesection 241 in the state where the actuator 1 is not driven. In suchcases, when the drive section 241 is rotated, (1) in the same state asthe non-driven state, the entire area of the flat plane of the slidingmember 42 is contacted with the drive section 241. (2) In the statewhere the driving source 4 is in the expanded state, the end of the flatplane of the sliding member 42 which is the closest to the central axisX of rotation makes a point contact or line contact with the drivesection 241. (3) In the state where the driving source 4 is in thecontracted state (that is, in the case where the driving source 5 is inthe expanded state), the end of the flat plane of the sliding member 42which is the farthest from the central axis X of rotation makes a pointcontact or line contact with the drive section 241. Based on what hasbeen described above, in the case where the sliding member 42 makes aplane contact with the drive section 241, the contact area therebetweenchanges, or the contact position of the drive section 241 with thesliding member 42 rapidly changes. This makes it difficult to smoothlyrotate the drive section 241.

The sliding member 42 is provided such that, in the direction parallelto the central axis X of rotation, the length of the distal end (i.e.,the portion to be contacted with the drive section 242) of the slidingmember 42 is longer than the length of the contact portion of the drivesection 242 with the sliding member 42, and such that the distal end ofthe sliding member 42 is contacted with the entire area of the drivesection 241. This enables the sliding member 42 to make a line contactwith the entire area of the drive section 241 in the direction parallelto the central axis X of rotation, even in the case where the couplingsection 24 expands or contracts caused by a change in temperature, andalong with the expansion and contraction the position of the drivesection 241 is displaced in the direction parallel to the central axis Xof rotation with respect to the sliding member 42. That is, this enablesrotating the drive section 241 while keeping the central axis X ofrotation fixed without being affected by change in temperature of theactuator 1.

In addition, the sliding member 42 makes a line contact with the entirearea of the drive section 241 in the direction parallel to the centralaxis X of rotation, which enables uniformly applying driving force ofthe driving source 4 to the entire area of the drive section 241 in thedirection parallel to the central axis X of rotation. In addition, thisreadily makes the contact portion between the driving source 4 and thedrive section 241 and the contact portion between the driving source 5and the drive section 241 symmetric with each other with respect to thecentral axis X of rotation. This results in enabling simplifyingmanufacture of the actuator 1 and rotating the drive section 241symmetrically with respect to the central axis X of rotation.

In this case, it is preferable that the contact pressure between thesliding member 42 and the drive section 241 be substantially 0 when theactuator 1 is not driven. This enables preventing displacement of thecentral axis X of rotation caused by warping of the coupling section 24in the direction perpendicular to the plane of the mass section 21. Notethat the structure is not particularly limited to the above, as long asthe driving force of the driving source 4 can be transmitted to thedrive section 241. For example, the structure may be such that thesliding member 42 is not contacted with the drive section 241 when theactuator 1 is not driven and the sliding member 42 is contacted with thedrive section 241 when the piezoelectric element 41 has expanded.

The distal end portion (i.e., the contact portion with the drive section241) of the sliding member 42 and the contact portion of the drivesection 241 with the sliding member 42 are surface treated to enhancesliding performance. This enables enhancing sliding performance of thedrive section 241 with respect to the sliding member 42. That is, thisenables reducing friction (sliding resistance) between the slidingmember 42 and the drive section 241. Specifically as shown in FIG. 2, acoating layer P is formed on each of the distal end portion of thesliding member 42 and the contact portion of the drive section 241 withthe sliding member 42.

Examples of materials that are capable of reducing such friction includepolyolefin such as polyethylene and polypropylene, polyvinyl chloride,polyester (such as PET, PBT), polyamide, polyimide, polyurethane,polystyrene, polycarbonate, silicone resin, fluorinated resin (such asPTFE, ETFE), and composite materials thereof.

Above all, in the case where a fluorinated resin (or a compositematerial including the same) is used, friction resistance between thesliding member 42 and the drive section 241 is reduced, whereby slidingperformance is enhanced.

In addition, in the case where fluorinated resin (or a compositematerial including the same) is used, the sliding member 42 and thedrive section 241 may be coated in the state where resin material hasbeen heated using a method such as baking and spraying. This providesparticularly superior adhesiveness of the coating layer P.

In addition, in the case where the coating layers P are formed ofsilicone resin (or a composite material including the same), reliablyand strongly adhered coating layers P can be formed without heating at atime of forming a coating layer P (i.e., coating the sliding member 42and the drive section 241). Specifically in the case where the coatinglayer P is formed of silicone resin (or a composite material includingthe same), reactive curing materials or the like can be used, and thusthe coating layer P can be formed at a room temperature. As describedabove, forming of the coating layer P at a room temperature makescoating simple.

Note that the surface treatments for enhancing sliding performance arenot limited to those described above. For example, the surface treatmentmay roughen the surface of the distal end portion of the sliding member42 and the surface of the contact portion of the drive section 241 withthe sliding member 42, respectively. In addition, in Embodiment 1,explanation has been given on the case where the coating layer P isformed on each of the distal end portion of the sliding member 42 andthe contact portion of the drive section 241 with the sliding member 42.However, at least either one of the two surfaces need be treated.Alternatively such a surface treatment may be omitted.

Such sliding member 42 has a lower heat conductivity than the componentof the piezoelectric element 41. This enables suppressing transmissionto the drive section 241 of heat which is generated by application ofvoltage to the piezoelectric element 41. This enables suppressingthermal expansion of the coupling section 24 caused by increasedtemperature.

Although such materials are not particularly limited, variousthermoplastic resins or various thermosetting resins may be used. Aboveall, it is particularly preferable that thermosetting resins be used.Thermosetting resins have good heat resistance and hardness and aredifficult to degenerate or denature. This enables preventing the slidingmember 42 from being deformed by heat generated by the piezoelectricelement 41. Such thermosetting resins are not particularly limited, and,for example, polyimide resins, phenol resins, epoxy resins, unsaturatedpolyester resins, urea resins, melamine resins, diallyl phthalate resinsor the like may be preferably used.

In addition, forming the sliding member 42 of a material capable ofreducing friction as described above enables omitting the process ofsurface treatment as described above, and thus simplifying themanufacturing process.

Hereinbefore, explanation has been given on the sliding member 42. Theshape of the sliding member 42 is not particularly limited, as long asthe shape enables driving the drive section 241. For example, thesliding member 42 may make a point contact with the drive section 241.As is the case with the line contact as described above, the pointcontact enables maintaining the contact area of the drive section 241with the sliding member 42 substantially constant when the drive section241 is rotated. In addition, this enables preventing the position of thecontact portion of the drive section 241 with the sliding member 42 fromrapidly changing during rotation of the drive section 241. This resultsin enabling rotating the drive section 241 smoothly and stably

Although explanation has been given on the driving source 4hereinbefore, the driving source 5 has a similar structure as thedriving source 4. Specifically the driving source 5 has thepiezoelectric element 51 and the sliding member 52. Such driving source4 and driving source 5 are provided such that they are symmetrical witheach other with respect to the central axis X of rotation. This enablesrotating the drive section 241 symmetrically with respect to the centralaxis X of rotation.

The actuator 1 with a structure as described above is driven asdescribed below.

For example, voltage as shown in FIG. 5A is applied to the piezoelectricelement 41, and voltage as shown in FIG. 5B is applied to thepiezoelectric element 51. Specifically, each of two voltages having 180°phase difference is applied to the piezoelectric element 41 and thepiezoelectric element 51. Next, the actuator 1 alternately repeats astate in which the piezoelectric element 41 is expanded and thepiezoelectric element 51 is contracted (i.e., the state is referred toas “the first state”) and a state in which the piezoelectric element 41is contracted and the piezoelectric element 51 is expanded (i.e., thestate is referred to as “the second state”).

In the first state, in FIG. 2, expansion of the piezoelectric element 41causes a portion to the left of the central axis X of rotation of thedrive section 241 to be inclined upwards and a portion to the rightthereof to be inclined downwards. That is, the drive section 241 isrotated clockwise in FIG. 2.

On the other hand, in the second state, in FIG. 2, expansion of thepiezoelectric element 51 causes a portion to the right of the centralaxis X of rotation of the drive section 241 to be inclined upwards and aportion to the left thereof to be inclined downwards. That is, the drivesection 241 is rotated counter-clockwise in FIG. 2.

Alternate repeating of such first state and second state enablesrotation of the drive section 241 around the central axis X of rotationwhile torsionally deforming the first elastic section 242, and alongwith the rotation, enables rotating the mass section 21 around thecentral axis X of rotation while torsionally deforming the secondelastic section 243. Note that expansion and contraction of thepiezoelectric elements 41, 51 in phases opposite to each other enablingrotating the drive section 241 while keeping the central axis X ofrotation fixed.

In addition, since driving force is obtained from the piezoelectricelements, the actuator 1 can be driven with relatively large drivingforce even when the actuator 1 is driven at low voltage drive. Thisenables enhancing a spring constant of the first elastic section 242 soas to drive the actuator at a high frequency even when the actuator 1 isdriven at low voltage drive.

Such actuator 1 can be manufactured, for example, as described below.

FIGS. 6 and 7 are diagrams (in longitudinal sectional view) fordescribing a method of manufacturing the actuator 1 according toEmbodiment 1, respectively Hereinafter, for convenience of description,in FIGS. 6 and 7, the front side of a plane of the drawing will bereferred to as “top,” and the back side thereof as “bottom.” Inaddition, the process of obtaining the base body 2 is referred to as“A1,” the process of obtaining the support substrate 3 as “A2,” theprocess of joining the driving sources 4, 5 to the support substrate 3as “A3,” and the process of joining the base body 2 to the supportsubstrate 3 as “A4.”.

A1

First, as shown in FIG. 6A, a silicon-on-insulator substrate (SOIsubstrate) 6 in which an Si layer 61, an SiO₂ layer 62, and an Si layer63 are sequentially laminated is prepared. Next, as shown in FIG. 6B, onthe top surface of the Si layer 61 of the SOI substrate 6, there isformed a resist mask 71 which has a shape corresponding to the shape inplan view of the mass section 21, the support section 22, and thecoupling section 24. On the other hand, on the bottom surface of the Silayer 63 of the SOI substrate 6, there is formed a resist mask 72 whichhas a shape corresponding to the shape in plan view of the supportsection 22 (space 28). Next, the SOI substrate 6 is etched via theresist mask 71. Subsequently the resist mask 71 is removed. In a similarmanner, the SOI substrate 6 is etched via the resist mask 72. At thistime, the SiO₂ layer 62 which is an intermediate layer of the SOIsubstrate 6 functions as a stop layer of etching as described above.

As an etching method, for example, one type may be used or more than onetype may be combined for use from a physical etching method such asplasma etching, reactive ion etching, beam etching, photo-assistedetching and a chemical etching method such as wet etching. Note that asimilar method may also be used in each of the following processes.

Subsequently the SiO₂ layer 62 is removed, and as shown in FIG. 6C, themass section 21, the support section 22 and the coupling section 24 maybe integrally formed.

Next, as shown in FIG. 6D, a metal film is formed on the top surface ofthe mass section 21 to form the light reflective section 211. Thisenables obtaining the base body 2. Examples of the method of forming themetal film (light reflective section 211) include a dry plating methodsuch as vacuum deposition, sputtering (low-temperature sputtering) andion plating, a wet plating method such as electrolytic plating andelectroless plating, a spraying method, joining of metallic foil and thelike.

A2

First, as shown in FIG. 7A, a silicon substrate 9 is prepared. Next, asshown in FIG. 7B, on the top surface of the silicon substrate 9, thereis formed a resist mask 73 which has a shape corresponding to theopening section 31 in plan view. Next, the silicon substrate 9 is etchedvia the resist mask 73. Subsequently the resist mask 73 is removed, andas shown in FIG. 7C, the support substrate 3 can be obtained.

A3

First, the piezoelectric element 41 is prepared. Subsequently thesliding member 42 is joined to the one end of the piezoelectric element41 in the directions in which the piezoelectric element 41 contracts andexpands, whereby the driving source 4 is obtained. Note that, as amanufacturing method of the piezoelectric element 41, for example, thepiezoelectric element 41 may be formed by for example, forming thepiezoelectric layer 411 having a certain thickness (length in thedirections in which the piezoelectric element 41 contracts and expands)and then by joining the thin-film based electrodes 412, 413 to bothsurfaces in the thickness direction, respectively. The same is appliedto the driving source 5.

Next, as shown in FIG. 7D, the surface of the driving source 4 oppositeto the sliding member 42 is joined to a portion corresponding to thedrive section 241 on the top surface of the support substrate 3. Thesame is applied to the driving source 5.

A4

Next, as shown in FIG. 7E, the bottom surface (i.e., support section 22)of the base body 2 obtained in the process “A1” is joined to the topsurface of the support substrate 3 on which there are provided thedriving sources 4, 5 obtained in the process “A3.” The joining method isnot particularly limited, and for example, anodic bonding may be usedfor joining. According to the manner as described above, the actuator 1of Embodiment 1 is manufactured.

Embodiment 2

Embodiment 2 of the actuator according to the invention will now bedescribed.

FIG. 8 is a partially sectional perspective view showing Embodiment 2 ofthe actuator according to the invention, FIG. 9 is a sectional view cutalong Line A-A in FIG. 8, and FIG. 10 is an expanded view of a drivingsource. Hereinafter, for convenience of description, in FIG. 8, thefront side of a plane of the drawing will be referred to as “top,” theback side thereof as “bottom,” the right side thereof as “right,” andthe left side thereof as “left.” In FIG. 9, the top side of a plane ofthe drawing will be referred to as “top,” the bottom side thereof as“bottom”, the right side thereof as “right,” and the left side thereofas “left.”

Hereinafter, for convenience of description, in FIG. 1, the front sideof a plane of the drawing will be referred to as “top,” the back sidethereof as “bottom,” the right side thereof as “right,” and the leftside thereof as “left.” For FIGS. 2 and 3, the top side of a plane ofthe drawing will be referred to as “top,” the bottom side thereof as“bottom”, the right side thereof as “right,” and the left side thereofas “left.”

Hereinafter, an actuator 1A of Embodiment 2 will be described focusingon the difference from the actuator 1 of Embodiment 1 as describedabove, and explanation on similar elements will be omitted.

The actuator 1A of Embodiment 2 is substantially same as the actuator 1of Embodiment 1, except the difference in the structure of a base body2A and in the shapes of a pair of driving sources 4A, 5A.

Specifically the base body 2A has a mass section 21A, a support section22A for supporting the mass section 21A and a coupling section 24A forcoupling the mass section 21A rotatably to the support section 22A.

The coupling section 24A has a branched section 241A which extends inthe direction perpendicular to the central axis X of rotation in planview of the mass section 21, a first elastic section 242A for couplingthe branched section 241A to the support section 22A, and a secondelastic section 243A for coupling the mass section 21A to the branchedsection 241A.

The first elastic section 242A includes a pair of elastic members 2421A,2422A which are provided so as to be opposed to each other with respectto the central axis X of rotation. The elastic member 2421A couples oneend of the branched section 241A in the direction in which the branchedsection 241A extends to the support section 22A, and the elastic member2422A couples the other end of the branched section 241A in thedirection in which the branched section 241A extends to the supportsection 22A. In addition, the elastic member 2421A and the elasticmember 2422A respectively extend in the direction parallel to thecentral axis X of rotation. That is, the coupling section 24A has astructure such that it is branched into two sections.

Such actuator 1A causes the piezoelectric element 41 to expand andcontract causing bending deformation of the elastic member 2421A, andcauses the piezoelectric element 51 to expand and contract causingbending deformation of the elastic member 2422A. Next, the actuator 1Acauses the piezoelectric element 41 and the piezoelectric element 51alternately expand and contract to rotate the branched section 244A.Along with the rotation, the actuator 1A rotates the mass section 21Awhile torsionally deforming the second elastic section 243A. At thistime, the mass section 21A is rotated centering around the central axisX of rotation shown in FIG. 8.

The driving source 4A is provided between the support substrate 3 andthe elastic member 2421A, is joined to the support substrate 3, and isslidable with respect to the elastic member 2421A. In a similar manner;the driving source 5A is provided between the support substrate 3 andthe elastic member 2422A, is joined to the support substrate 3, and isslidable with respect to the elastic member 2422A.

The driving sources 4A, 5A will now be described in details. Since thedriving source 4A and the driving source 5A have similar structures(including shapes and dimensions), explanation will be given on thedriving source 4A as a representative, and explanation on the drivingsource 5A will be omitted.

The driving source 4A, as shown in FIG. 10, includes the piezoelectricelement 41 and the sliding member 42A. The piezoelectric element 41 hasa columnar structure which expands and contracts in the longitudinaldirection thereof, and it is provided such that it expands and contractsin a direction perpendicular to a plane of the drive section 241 whenthe actuator 1A is not driven (i.e., in the vertical direction in FIG.9). Furthermore, the bottom surface of the piezoelectric element 41 isjoined to the support substrate 3.

On the top surface of such piezoelectric element 41, there is providedthe sliding member 42A. The sliding member 42A is joined to thepiezoelectric element 41, and is slidable with respect to the elasticmember 2421A.

Such sliding member 42A makes a point contact with the elastic member2421A. This enables enhancing following capability of the sliding member42A with respect to rotation of the drive section 2421A when thepiezoelectric element 41 is caused to expand and contract. Specificallymainly bending deformation is generated in the elastic member 2421Abecause of expansion and contraction of the piezoelectric element 41.Since the branch section is rotated along with the expansion andcontraction, slight torsional deformation is also generated. Therefore,making a point contact of the sliding member 42 with the elastic member2421A enables causing bending deformation of the elastic member 2421Awithout being affected by torsional deformation of the elastic member2421A.

Hereinbefore, explanation has been given on the actuators according tothe embodiments of the invention. Since the actuators according to theinvention include a light reflective section, they may be applied to anoptical device such as an optical scanner, an optical switch, and anoptical attenuator.

As is the case with the actuator 1 according to the embodiment of theinvention, an optical scanner 1B according to the embodiments of theinvention has a mass section, a light reflective section provided in themass section, a support section, a coupling section for supporting themass section with cantilever structure, and a pair of driving sourceswhich are provided slidably with respect to the coupling section. Suchoptical scanner causes the piezoelectric element each driving source hasto expand and contract in the phases opposite to each other totorsionally deform at least a part of the coupling section, causingrotating the mass section and scanning a light beam by the lightreflective section. The structure of the coupling section and thestructure of each driving source are similar to those of the actuator 1according to the embodiment of the invention. This enables permittingthe coupling section from being displaced because of thermal expansionin the direction parallel to the central axis of rotation of the masssection. This results in enabling preventing a rapid change in a springconstant of the coupling section, and further keeping the central axisof rotation of the mass section fixed. Accordingly the optical scanneraccording to the embodiment of the invention is capable of havingdesired scan characteristics even in the cases such as where a lightbeam exceeding the light beam which was able to be reflected by thelight reflective section 211 has increased the temperature of theoptical scanner or where heat emitted by the piezoelectric elements hasincreased the temperature of the optical scanner. That is, the opticalscanner according to the embodiment of the invention is capable ofmaintaining desired scan characteristics even in the case where it isused continuously for a long period of time.

Such an optical scanner may be preferably applied to an image formingapparatus, such as a laser printer, an imaging display a bar-codereader, and a confocal scanning microscope. This results in enablingproviding the image forming apparatus having superior drawingcharacteristics.

Specifically a laser printer as shown in FIG. 11 will be explained.

A laser printer (i.e., image forming apparatus) 8 of the presentembodiment as shown in FIG. 11 records an image in a recording mediumthrough a series of image forming processes mainly including exposure,development, transfer and fixation. Such image forming apparatus 8, asshown in FIG. 11, has a photoreceptor 81 which carries an electrostaticlatent image and which is rotated in a direction shown by an arrow, andin the image forming apparatus 8. In addition, a charged unit 82, anexposure unit 83, a development unit 84, a primary transfer roller 851,and a cleaning unit 86 are sequentially arranged along the direction inwhich the photoreceptor is rotated. In addition, at the lower portion ofthe laser printer 8 shown in FIG. 11, there is arranged a paper feedtray 87 for accommodating a recording medium such as paper. Downstreamof the paper feed tray 87 in the direction in which the recording mediumis transferred, there are sequentially arranged a secondary transferroller 88, and a fixation unit 89 along the direction in which therecording medium is transferred.

The photoreceptor 81 has a cylindrical conducting base material (notshown) and a photosensitive layer (not shown) formed on the peripheralsurface thereof, and is rotatable around the axis line thereof in thedirection shown by the arrow in FIG. 11.

The charged unit 82 is an apparatus for uniformly charging the surfaceof the photoreceptor 81 using corona electrification or the like.

The exposure unit 83 is an apparatus which receives image informationfrom a host computer such as a personal computer, not shown, andirradiates a laser beam on the uniformly charged photoreceptor(photoconductive drum) 81 in response to the image information, therebyforming an electrostatic latent image. Specifically as shown in FIG. 12,the exposure unit 83 has the optical scanner 1B according to theembodiment of the invention, a light source 831 for irradiating a lightbeam to the light reflective section of the optical scanner 1B, a focuslens 832 for focusing a light beam which has been irradiated from thelight source 831 to the light reflective section, and an f θ lens 833for changing a speed of the light beam reflected by the light reflectivesection. This enables the exposure unit 83 to scan (irradiate) a lightbeam at a desired scanning position of the object to be scanned(photoreceptor 81), thereby enables forming a desired latent image. As aresult of this, the image forming apparatus according to the embodimentof the invention is capable of having superior drawing characteristics.Note that the structure of the exposure unit 83 is not limited to this.

The development unit 84 has four development units: a black developmentunit 841, a magenta development unit 842, a cyan development unit 843,and a yellow development unit 844, and is rotatable so as to be opposedto the photoreceptor 81.

The operation the laser printer 8 with a structure as described abovewill now be described.

First, the photoreceptor 81, the development roller (not shown) providedon the development unit 84, and an intermediate transfer belt 852 startrotation triggered by a command from the host computer, not shown. Next,the photoreceptor 81 is sequentially charged by the charged unit 82,while it is being rotated.

A charged area of the photoreceptor 81 reaches an exposure positionalong with the rotation of the photoreceptor 81. A latent imagecorresponding to the image information for the first color, for exampleyellow Y, is formed in the area by the exposure unit 83.

The latent image formed on the photoreceptor 81 reaches a developmentposition along with the rotation of the photoreceptor 81, and isdeveloped by the yellow development unit 844 on the yellow toner. Thisforms a yellow toner image on the photoreceptor 81. At this time, in theYMCK development unit 84, the yellow development unit 844 is opposed tothe photoreceptor 81 at the development position.

The yellow toner image formed on the photoreceptor 81 reaches a primarytransfer position (that is, the portion at which the photoreceptor 81 isopposed to the primary transfer roller 851) along with the rotation ofthe photoreceptor 81, and is transferred (i.e., primarily-transferred)to the intermediate transfer belt 852 by the primary transfer roller851. At this time, primary transfer voltage (i.e., primary transferbias) with a polarity opposite to the charge characteristics of thetoner is applied to the primary transfer roller 851. Note that, duringthis period of time, the secondary transfer roller 88 is separated fromthe intermediate transfer belt 852.

The processing similar to that described above is repeatedly carried outfor the second color, the third color and the fourth color, wherebytoner images for respective colors corresponding to respective imagesignals are transferred on the intermediate transfer belt 852 in amanner such that the toner images are overlapped with each other. Thisenables forming a full-color toner image on the intermediate transferbelt 852.

Meanwhile, the recording medium is transferred from the paper feed tray87 to the secondary transfer roller 88.

The full-color toner image formed on the intermediate transfer belt 852reaches a secondary transfer position (that is, the portion at which thesecondary transfer roller 88 is opposed to the drive roller 853) alongwith rotation of the intermediate transfer belt 852, and is transferred(i.e., secondarily-transferred) on a recording medium P by the secondarytransfer roller 88. At this time, the secondary transfer roller 88 ispressed to the intermediate transfer belt 852, and secondary transfervoltage (i.e., secondary transfer bias) is applied to the secondarytransfer roller 88.

The full-color toner image transferred on the recording medium is heatedand pressurized by the fixation unit 89 so as to be fused to therecording medium P. Subsequently the recording medium is ejected tooutside of the laser printer 8.

Meanwhile, after the photoreceptor 81 has passed the primary transferposition, the toner attached to the surface thereof is scraped off by acleaning blade 861 of the cleaning unit 86, and then the photoreceptor81 gets ready for a charge for forming a next latent image. The tonerwhich has been scraped off is collected by a residual toner collectionsection in the cleaning unit 86.

Hereinbefore, the actuator, the optical scanner and the image formingapparatus according to the invention have been described referring tothe embodiments as shown in the drawings. However, the invention is notlimited to this.

For example, a structure for each section of the actuator according tothe embodiment of the invention may be replaced by one with arbitrarystructure which has similar functions, or arbitrary structure may beadded to the actuator.

Furthermore, in the embodiments described above, the elastic member hasa linear shape. However, as long as the drive section can be rotated bycausing bending deformation of a pair of elastic members in thedirections opposite to each other, the elastic member may have anarbitrary shape.

Furthermore, in the embodiments described above, the structure having ashape substantially symmetrical (i.e., bilaterally symmetrical) withrespect to the plane which passes through the center of the actuator andwhich is perpendicular to the rotation axis line of the mass section andthe pair of drive sections has been described. However, the structuremay instead be asymmetrical.

Furthermore, in the embodiments described above, the structure in whichthe light reflective section is provided on the top surface of the masssection has been described. However, the structure may have a structure,for example, it provided in the opposite manner. That is, the lightreflective section may be provided on the back side of the mass section.

1. An actuator comprising: a mass section; a support section; a couplingsection for coupling the mass section rotatably to the support sectionso as to support the mass section with cantilever structure; and a pairof driving sources including a piezoelectric element for rotating themass section, wherein the pair of driving sources are providedseparately from each other with respect to a central axis of rotation ofthe mass section, each of the driving sources is provided slidably withrespect to the coupling section or the support section, and the actuatoris structured such that the actuator causes the pair of piezoelectricelements to expand and contract in phases opposite to each other, so asto rotate at least a part of the coupling section while torsionallydeforming the mass section.
 2. The actuator according to claim 1,wherein each of the driving sources is secured to the support sectionand further includes a sliding member between the piezoelectric elementand the coupling section, and the sliding member is joined to thepiezoelectric element on which the sliding member is provided and isslidable with respect to the coupling section.
 3. The actuator accordingto claim 2, wherein the sliding member has a lower heat conductivitythan a primary component of the piezoelectric element.
 4. The actuatoraccording to claim 1, wherein surface treatment is provided on a surfaceof an abutting section of each of the driving sources with the couplingsection and/or a surface of the abutting section of the coupling sectionwith each of the driving sources to enhance sliding performance.
 5. Theactuator according to claim 1, wherein the coupling section has aplate-shaped drive section, a first elastic section for coupling thedrive section rotatably to the first support section, and a secondelastic section for coupling the mass section rotatably to the drivesection, and each of the driving sources is provided slidably withrespect to the drive section.
 6. The actuator according to claim 5,wherein each of the driving sources makes a point contact with the drivesection, or makes a line contact therewith so that it extends in adirection parallel to the central axis of rotation of the mass section.7. The actuator according to claim 6, wherein each of the drivingsources makes a line contact with the entire area of the drive sectionin the direction parallel to the central axis of rotation of the masssection.
 8. The actuator according to claim 5, wherein the pair ofdriving sources are provided substantially symmetrically with each otherwith respect to the central axis of rotation of the mass section in planview of the drive section.
 9. The actuator according to claim 1, whereinthe elastic section has a pair of elastically deformable elastic membersthat are opposed to each other with respect to the central axis ofrotation of the mass section, the pair of driving sources are providedcorresponding to the pair of elastic members, respectively and thedriving source and the elastic member that correspond to each other areslidably provided.
 10. The actuator according to claim 9, wherein eachof the driving sources makes a point contact with the elastic member.11. The actuator according to claim 1, wherein the mass section includesa light reflective section having light reflectivity.
 12. An opticalscanner comprising: a mass section; a support section; a couplingsection for coupling the mass section rotatably to the support sectionso as to support the mass section with cantilever structure; and a pairof driving sources including a piezoelectric element for rotating themass section, wherein the pair of driving sources are providedseparately from each other with respect to a central axis of rotation ofthe mass section, each of the driving sources is provided slidably withrespect to the coupling section or the support section, and the opticalscanner is structured such that it causes the pair of piezoelectricelements to expand and contract in phases opposite to each other, so asto rotate at least a part of the coupling section while torsionallydeforming the mass section, and scans a light beam reflected by thelight reflective section.
 13. An image forming apparatus comprising anoptical scanner including: a mass section; a support section; a couplingsection for coupling the mass section rotatably to the support sectionso as to support the mass section with cantilever structure; and a pairof driving sources including a piezoelectric element for rotating themass section, wherein the pair of driving sources are providedseparately from each other with respect to a central axis of rotation ofthe mass section, each of the driving sources is provided slidably withrespect to the coupling section or the support section, and the opticalscanner is structured such that it causes the pair of piezoelectricelements to expand and contract in phases opposite to each other, so asto rotate at least a part of the coupling section while torsionallydeforming the mass section, and scans a light beam reflected by thelight reflective section.